BOSTON (CBS) — Since the postseason began, it didn’t matter when or where you saw Jon Lester. Everywhere he went, he wore his game face at all times.

Whether he was on the mound against the Rays, Tigers or Cardinals, whether he was answering an endless stream of questions from the media, or whether he was calmly holding his son while standing on the field in the middle of an ALCS celebration, the only thing you’ve seen from Lester this October has been his game face.

It has been clear that Lester understood his responsibility as the Red Sox’ No. 1 starting pitcher, and all he’s done since the playoffs began is get his job done.

That culminated for Lester on Monday night in Game 5 of the World Series. Matched up against Cardinals ace Adam Wainwright for the second time in a week, Lester and the Red Sox wouldn’t be gifted free early runs from defensive blunders by the Cardinals, but he didn’t need them. The 29-year-old mowed down the Cardinals, making just one mistake over his 7 2/3 innings of work.

He showed little emotion — good or bad — all night long, but when he walked off the mound with two outs in the eighth inning, he knew that he had done his job.

“Given the stage, given how strong he’s been throughout the course of this year, and particularly the second half and what he’s doing in his own right career‑wise in the postseason, yeah, this was a big game,” manager John Farrell said of his starter. “Jon Lester was fantastic tonight.”

Lester allowed just one earned run — a solo homer by Matt Holliday in the fourth — on the night, recording two outs in the eighth inning before handing the baseball to closer Koji Uehara, who retired all four men he faced to seal the 3-1 victory.

The Game 5 performance was a continuation of what Lester’s been able to do all postseason for Boston. He’s allowed just 33 men to reach base in 34 2/3 innings, striking out 29 batters and allowing just six earned runs for a 1.56 ERA. And he did it on Monday despite dealing with some back tightness, which Farrell described after the game. Given that fellow pitcher Clay Buchholz hasn’t had the same ability to pitch through pain, and given that Shane Victorino finally was forced out of the lineup due to back pain of his own, that’s a feat that shouldn’t go unnoticed for Lester.

The playoff excellence isn’t anything new for Lester, who is now 3-0 in his career in the World Series. He owns a 2.11 ERA in 13 postseason appearances, and he became just the fifth pitcher in history to allow one or fewer runs in his first three World Series starts, the first to do it since the 1940s.

David Ortiz, on an unheard-of postseason run of his own, said that when Lester came into the big leagues seven years ago, he absorbed the winning culture and dedicated himself to being a part of it.

David Ortiz welcomes Jon Lester to the dugout in Game 5. (Photo by Rob Carr/Getty Images)

“Jon, he came up to the big leagues at the time where we were going to the playoffs and winning World Series. As a young player, he’s always looking around and trying to improve himself and get better,” Ortiz said. “I’m pretty sure that him watching those guys when we won in 2007, and you guys saw his performance that year, as a player he told me straight up he was going to be the future ace of this organization. And there he is, doing what he does best.”

Farrell has become familiar with Lester’s game face, and when he was asked if he saw any clues in particular from the pitcher that might hint to such a performance, the manager’s answer suggested that he only saw the same guy who’s been showing up since the start of October.

“The clues have been every time he’s walked out in the postseason,” Farrell said. “That’s the clue we look at.”

He’s carried the team through matchups against Wainwright, Matt Moore and Anibal Sanchez, and while he hasn’t done it alone, the Red Sox likely wouldn’t be sitting pretty, one win away from a championship, if Lester hadn’t put together this run of dominance. But he has, and so they are.

If the Red Sox can finish the job in Game 6 or 7, Lester may finally ease up with that stoic intensity and let loose in the middle of a celebratory dogpile. He’s certainly earned that right.